Cleaning method and polishing apparatus employing such cleaning method

ABSTRACT

A method is suitable for cleaning substrates, after polishing, that require a high degree of cleanliness, such as semiconductor wafers, glass substrates, or liquid crystal displays. The method comprises polishing a substrate using an abrasive liquid containing abrasive particles, and cleaning a polished surface of the substrate by supplying a cleaning liquid having substantially the same pH as the abrasive liquid or similar pH to the abrasive liquid so that a pH of the abrasive liquid attached to the polished surface of the substrate is not rapidly changed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a cleaning method and apolishing apparatus employing such cleaning method, and moreparticularly to a cleaning method suitable for cleaning substrates thatrequire a high degree of cleanliness, such as semiconductor wafers,glass substrates, or liquid crystal displays, and to a polishingapparatus employing such cleaning method.

[0003] 2. Description of the Related Art

[0004] As semiconductor devices have become more highly integrated inrecently years, circuit interconnections on semiconductor substratesbecome finer and the distances between those circuit interconnectionshave become smaller. One of the processes available for forming suchcircuit interconnections is photolithography. In the case where circuitinterconnections are formed by the photolithography or the like, itrequires that surfaces on which patterns images are to be focused by astepper be as flat as possible because the depth of focus of the opticalsystem is relatively small.

[0005] It is therefore necessary to make the surfaces of semiconductorsubstrates flat for photolithography. One customary way of flatteningthe surfaces of the semiconductor substrates is to polish them with apolishing apparatus. As shown in FIG. 8, a conventional polishingapparatus 76 comprises a turntable 72 having a polishing cloth 70thereon, and a top ring 74 for holding a semiconductor substrate W andpressing the semiconductor substrate W against the turntable 72. In thepolishing apparatus, a chemical mechanical polishing (CMP) of thesubstrate is performed by a combination of chemical polishing with anabrasive liquid and mechanical polishing with abrasive particlescontained in the abrasive liquid. An abrasive liquid supply nozzle 78 isprovided above the turntable 72 to supply the abrasive liquid Q to thepolishing cloth 70. Further, a dressing device 80 is provided toregenerate, i.e. dress the polishing cloth 70.

[0006]FIG. 9 shows a CMP unit which is constructed as an integral unithaving the polishing apparatus 76 shown in FIG. 8 and various devicesassociated with the polishing apparatus 76. The CMP unit has asubstantially rectangular shape in plan, and the polishing apparatus 76is disposed at one side of the CMP unit, and load and unload units 84 a,84 b for placing wafer cassettes which accommodate semiconductorsubstrates to be polished are disposed at the other side of the CMPunit. Transfer robots 86 a, 86 b are movably provided between thepolishing apparatus 76 and the load and unload units 84 a, 84 b so thatthe transfer robots 86 a, 86 b are movable along a transfer line C.Reversing devices 88 a, 88 b for reversing a semiconductor substrate aredisposed at one side of the transfer line C, and cleaning apparatuses 90a, 90 b, 90 c for cleaning the semiconductor substrate are disposed atthe other side of the transfer line C. A pusher 10 is disposed adjacentto the turntable 72 to transfer the semiconductor substrate between thetop ring 74 and the pusher 10 by vertical movement thereof.

[0007] In the polishing apparatus 76 having the above structure, thesemiconductor substrate W is held by the lower surface of the top ring74 and pressed against the polishing cloth 70 on the turntable 72. Theabrasive liquid Q is supplied from the abrasive liquid supply nozzle 78onto the polishing cloth 70 and retained on the polishing cloth 70.During operation, the top ring 74 exerts a certain pressure on theturntable 72, and the surface of the semiconductor substrate heldagainst the polishing cloth 70 is therefore polished in the presence ofthe abrasive liquid Q between the surface of the semiconductor substrateW and the polishing cloth 70 by a combination of chemical polishing andmechanical polishing while the top ring and the turntable are rotated.The abrasive liquid Q contains various abrasive particles, and the pH ofthe abrasive liquid Q is adjusted in accordance with the kind ofsemiconductor substrates to be polished.

[0008] As described above, as semiconductor devices have become morehighly integrated, circuit interconnections on semiconductor substratesbecome finer and the distances between those circuit interconnectionshave become smaller. Therefore, in the above polishing process, if aparticle greater than the distance between interconnections adheres to asemiconductor substrate and thus such particle remains on the product,i.e. semiconductor device, then the particle will short-circuitinterconnections on the semiconductor device. Therefore, any undesirableparticles on the semiconductor substrate have to be sufficiently smallerthan the distance between interconnections on the semiconductorsubstrate. Such a problem and a requirement hold true for the processingof other substrates including a glass substrate to be used as a mask, aliquid crystal panel, and so on.

[0009] In the above-mentioned CMP process, the semiconductor substratewhich has been polished is transferred to the cleaning apparatuses 90 a,90 b and 90 c. In the cleaning apparatuses 90 a, 90 b and 90 c, forexample, a scrubbing cleaning process in which a cleaning member such asa brush or a sponge is used to scrub a surface of the semiconductorsubstrate while supplying a cleaning liquid such as pure water, and aspinning dry process subsequent to the scrubbing cleaning process areperformed, and the abrasive particles or the ground-off particlesattached to the semiconductor substrate during the polishing process areremoved from the semiconductor substrate.

[0010] When pure water (deionized water) is supplied to thesemiconductor substrate which has been polished, the pH of the abrasiveliquid remaining on the semiconductor substrate changes greatly.Therefore, in some cases, abrasive particles which have been dispersedin the abrasive liquid having an original pH are aggregated together,and adhere to the surface of the semiconductor substrate. For example,in slurry of colloidal silica which is generally used for polishing Sio₂layer, silica particles which are abrasive particles are stable inalkali solution having a pH of about 10, and form secondary particleshaving a diameter of about 0.2 μm due to aggregation of primary silicaparticles. If this slurry is rapidly diluted with pure water to lowerthe pH of the slurry to 7 or 8, then the electric potential on thesurfaces of silica particles is rapidly changed by so-called pH shock,and the silica particles become unstable to thus aggregate the secondaryparticles to form larger aggregates. In this specification, the pH shockis defined as a rapid change of a pH. This holds true for the dressingprocess of the polishing cloth 70. To be more specific, when pure wateras a dressing liquid is supplied onto the polishing cloth 70 holding theabrasive liquid Q thereon, the pH of the abrasive liquid is rapidlylowered to cause abrasive particles to aggregate. These aggregatesremain on the polishing cloth 70 and cause the semiconductor substrateto form scratches in the polishing process.

SUMMARY OF THE INVENTION

[0011] It is therefore an object of the present invention to provide acleaning method which can efficiently perform cleaning of substrateswhich have been polished without causing abrasive particles contained inan abrasive liquid to be aggregated.

[0012] Another object of the present invention is to provide a dressingmethod which can efficiently perform dressing of a polishing surface ona turntable without causing abrasive particles contained in an abrasiveliquid to be aggregated on the polishing surface.

[0013] Still another object of the present invention is to provide apolishing apparatus employing such cleaning method or dressing method.

[0014] According to a first aspect of the present invention, there isprovided a method for polishing and then cleaning a substrate, themethod comprising: polishing a substrate using an abrasive liquidcontaining abrasive particles; and cleaning a polished surface of thesubstrate by supplying a cleaning liquid having substantially the samepH as the abrasive liquid or similar pH to the abrasive liquid so that apH of the abrasive liquid attached to the polished surface of thesubstrate is not rapidly changed.

[0015] In the present invention, when using silica slurry having a pH ofabout 10 as an abrasive liquid, the cleaning liquid whose pH is in therange of 9 to 11 may be used.

[0016] According to the present invention, the pH of the abrasive liquidattached to the substrate in the polishing process is not rapidlychanged, and hence cleaning of the substrate is conducted in such astate that the abrasive particles are not aggregated due to pH shock.This cleaning process of the substrate is performed in the case whereliquid other than the abrasive liquid is first supplied to the surfaceof the substrate after the polishing process of the substrate. Thiscleaning process includes rinsing of the substrate on the turntable orin the vicinity of the turntable by supplying a cleaning liquid to thesubstrate, and a scrubbing cleaning in which the substrate is scrubbedby a cleaning member while supplying a cleaning liquid to the substratein a cleaning apparatus.

[0017] According to a second aspect of the present invention, there isprovided a method for polishing and then cleaning a substrate, themethod comprising: polishing a substrate using an abrasive liquidcontaining abrasive particles; and cleaning a polished surface of thesubstrate by supplying a cleaning liquid whose pH is changed during thecleaning.

[0018] In a preferred aspect, the pH of the cleaning liquid is changedfrom acid or alkali to neutrality. Thus, the substrate may betransferred to the next process in a stable neutral condition.

[0019] According to a third aspect of the present invention, there isprovided a method for polishing a substrate and then dressing apolishing surface on a turntable, the method comprising: polishing asubstrate using an abrasive liquid containing abrasive particles bycontacting the substrate with the polishing surface; and dressing thepolishing surface by supplying a dressing liquid having substantiallythe same pH as the abrasive liquid or similar pH to the abrasive liquidso that a pH of the abrasive liquid on the polishing surface is notrapidly changed.

[0020] According to the present invention, the polishing surface on theturntable may be dressed in such a state that the abrasive particles arenot aggregated on the polishing surface.

[0021] In a preferred aspect, the cleaning liquid or the dressing liquidcomprises electrolytic ionic water. Thus, contamination of the substratecaused by metal ion may be prevented and adjustment of the pH of theabrasive liquid may be made.

[0022] According to a fourth aspect of the present invention, there isprovided an apparatus for polishing and then cleaning a substrate, theapparatus comprising: a polishing apparatus for polishing a substrateusing an abrasive liquid containing abrasive particles; and a cleaningapparatus for cleaning a polished surface of the substrate by supplyinga cleaning liquid having substantially the same pH as the abrasiveliquid or similar pH to the abrasive liquid so that a pH of the abrasiveliquid attached to the polished surface of the substrate is not rapidlychanged.

[0023] According to a fifth aspect of the present invention, there isprovided an apparatus for polishing and then cleaning a substrate, theapparatus comprising: a polishing apparatus for polishing a substrateusing an abrasive liquid containing abrasive particles; and a cleaningapparatus for cleaning a polished surface of the substrate by supplyinga cleaning liquid whose pH is changed during the cleaning.

[0024] According to a sixth aspect of the present invention, there isprovided an apparatus for polishing a substrate and then dressing apolishing surface on a turntable, the apparatus comprising: a polishingapparatus for polishing a substrate using an abrasive liquid containingabrasive particles by contacting the substrate with the polishingsurface; and a dressing apparatus for dressing the polishing surface bysupplying a dressing liquid having substantially the same pH as theabrasive liquid or similar pH to the abrasive liquid so that a pH of theabrasive liquid on the polishing surface is not rapidly changed.

[0025] The above and other objects, features, and advantages of thepresent invention will become apparent from the following descriptionwhen taken in conjunction with the accompanying drawings whichillustrate preferred embodiments of the present invention by way ofexample.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a cross-sectional view of a primary cleaning apparatusaccording an embodiment of the present invention;

[0027]FIG. 2A is a plan view of a workpiece support in the primarycleaning apparatus shown in FIG. 1;

[0028]FIG. 2B is a cross-sectional view taken along line II-II of FIG.2A;

[0029]FIG. 3 is a perspective view of a cover in the primary cleaningapparatus shown in FIG. 1;

[0030]FIG. 4 is a schematic flow diagram of a cleaning liquid supplysystem;

[0031]FIG. 5 is a cross-sectional view of the primary cleaningapparatus;

[0032]FIG. 6 is a graph showing the change of pH in the cleaning liquidin the primary cleaning process;

[0033]FIG. 7 is a front view of the polishing apparatus in which adressing process is carried out;

[0034]FIG. 8 is a front view of a conventional polishing apparatus; and

[0035]FIG. 9 is a plan view of the conventional polishing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] A polishing apparatus which uses a cleaning method of the presentinvention will be described with reference to FIGS. 1 through 7. Thewhole structure of the polishing apparatus in the present invention isthe same as the conventional polishing apparatus shown in FIGS. 8 and 9,and hence the detailed description thereof is not made.

[0037] As shown in FIGS. 1 through 3, the polishing apparatus of thepresent invention comprises a substrate transferring apparatus (pusher)10 in which a primary cleaning apparatus C for primarily cleaning asemiconductor substrate which has been polished is provided. Thisprimary cleaning process is defined as a cleaning process for cleaningor rinsing a polished substrate, for the first time, by supplying liquidother than the abrasive liquid. The pusher 10 comprises a workpiecesupport 12 for placing a semiconductor substrate thereon, and anactuator unit 14 for vertically moving the workpiece support 12. Theworkpiece support 12 is supported on the upper ends of vertical rods 15that are vertically movably provided from the actuator unit 14. In FIG.1, the semiconductor substrate W is shown as being held by the top ring74, and the workpiece support 12 is shown as being lowered. The pusher10 further comprises a water receiving container 18 provided around thepusher 10 and having a drain port 16, and a nozzle bracket 20 attachedto the inside of the container 18 for mounting nozzle units thereon.

[0038] As shown in FIGS. 2A and 2B, the workpiece support 12 has acircular base 22, and a pair of arcuate holding plates 24 mounted on anouter circumferential edge of the circular base 22 and spaced from eachother by a pair of recesses 26 defined therebetween. The recesses 26serve to receive the arm (not shown) of the transfer robot 86 b (seeFIG. 9) for transferring the semiconductor substrate W between theholding plates 24 and the transfer robot 86 b. Three nozzle units 28,30, 32 are mounted on the nozzle bracket 20. The upper nozzle unit 28serves to eject a cleaning liquid to the lower surface of the top ring74, the middle nozzle unit 30 serves to eject a cleaning liquid to theupper surface of the semiconductor substrate W placed on the workpiecesupport 12, and the lower nozzle unit 32 serves to eject a cleaningliquid to the lower surface of the semiconductor substrate W placed onthe workpiece support 12 through the recess 26 of the workpiece support12.

[0039] These nozzle units 28, 30 and 32 may eject a cleaning liquidhaving a pressure of 1.1 to 1.2 kg/cm² or a cleaning liquid to whichultrasonic wave is imparted by an ultrasonic wave generating apparatus.

[0040] As shown in FIG. 2A, the nozzle unit 32 comprising a plurality ofnozzles 32 a is disposed at one location along a circumferentialdirection of the workpiece support 12, but a plurality of nozzle unitsmay be disposed at a plurality of locations along a circumferentialdirection of the workpiece support 12. The nozzle units 28 and 30 may bealso disposed in the same manner as the nozzle unit 32.

[0041] As shown in FIG. 1, a cover 34 for preventing a cleaning liquidejected from the cleaning nozzle units 28, 30 and 32 from beingscattered around is provided so as to enclose a space around the pusher10. As shown in FIG. 3, the cover 34 has a window 36 for allowing thetop ring 74 to pass therethrough on one side thereof, and a window 38for allowing the arm (not shown) of the robot 86 b (see FIG. 9) to passtherethrough on the other side thereof.

[0042] As shown in FIG. 4, a cleaning liquid supply apparatus 40 isprovided to supply a cleaning liquid to the nozzle units 28, 30 and 32in the primary cleaning apparatus C. The cleaning liquid supplyapparatus 40 comprises a first cleaning liquid tank 42 for storing afirst cleaning liquid having a pH of a certain value, and a secondcleaning liquid tank 44 for storing a second cleaning liquid which isneutral. In the case where an abrasive liquid used in the polishingprocess is silica slurry, the first cleaning liquid has a pH of about10. The cleaning liquid supply apparatus 40 further comprises flowregulating valves 48 a, 48 b provided in pipes 46 a, 46 b extending fromthe respective cleaning liquid tanks 42 and 44, a pipe 50 connected tothe pipes 46 a, 46 b at the downstream sides of the flow regulatingvalves 48 a, 48 b, pipes 54 a, 54 b and 54 c branched from the pipe 50,and valves 52 a, 52 b and 52 c provided in the respective pipes 54 a, 54b and 54 c. The pipes 54 a, 54 b and 54 c are connected to therespective nozzle units 28, 30 and 32. The opening degrees of the flowregulating valves 48 a, 48 b may be adjusted by a controller or a timerso that first, only the first cleaning liquid is supplied, after acertain period of time has elapsed, the second cleaning liquid starts tobe supplied and the ratio of the second cleaning liquid to the firstcleaning liquid is gradually increased, and finally, only the neutralsecond cleaning liquid is supplied.

[0043] In the above embodiment, the pH of the first cleaning liquid isabout 10, and KOH or the like is used for adjusting a pH of the firstcleaning liquid. If the cleaning liquid having a pH of about 9 issufficient to prevent pH shock from occurring, then electrolytic ionicwater which is obtained by electrolysis using an ion exchange membranemay be used. In this case, metal ion is not contained in the cleaningliquid, and hence there is little chance of contamination of thesubstrate.

[0044] Next, processes in the polishing apparatus having the abovestructure will be described with reference to drawings.

[0045] As shown in FIG. 8, the semiconductor substrate W is held undervacuum by the top ring 74, and pressed against the polishing cloth 70 onthe turntable 72 while the abrasive liquid Q is supplied onto thepolishing cloth 70. The polishing cloth 70 constitutes a polishingsurface on the turntable 72. While the turntable 72 and the top ring 74are rotated independently of each other, the lower surface of thesemiconductor substrate W is polished to a flat mirror finish. After thesemiconductor substrate W is polished, the ground-off particles and theabrasive liquid Q containing abrasive particles adhere to thesemiconductor substrate W and the top ring 74. After completingpolishing of the semiconductor substrate W, the top ring 74 which holdsthe semiconductor substrate W under the vacuum is angularly moved abovethe pusher 10, and the top ring 74 is located at the primary cleaningposition inside the cover 34 as shown in FIG. 1. While the top ring 74holds the semiconductor substrate W, a cleaning liquid is supplied fromthe upper nozzle unit 28 to thereby clean the polished surface of thesemiconductor substrate W. In this case, only the first cleaning liquidis supplied from the first cleaning liquid tank 42 to the semiconductorsubstrate.

[0046] Then, the actuator unit 14 of the pusher 10 is operated to liftthe workpiece support 12 toward the top ring 74. Thereafter, thesemiconductor substrate W is removed from the top ring 74 by breakingvacuum and placed on the workpiece support 12. The actuator unit 14 isoperated again to lower the workpiece support 12 away from the top ring74 as shown in FIG. 5. Then, the three cleaning nozzle units 28, 30 and32 are simultaneously operated to eject the cleaning liquid for therebycleaning the upper and lower surfaces of the semiconductor substrate Wand the lower surface of the top ring 74. In this case, as shown in FIG.6, first, the first cleaning liquid is supplied from the first cleaningliquid tank 42, and after a certain period time, the second cleaningliquid starts to be supplied from the second cleaning liquid tank 44 andthe ratio of the second cleaning liquid to the first cleaning liquid isgradually increased. Finally, only the cleaning liquid of pH 7 issupplied from the second cleaning liquid tank 44.

[0047] In this manner, in the early cleaning stage, the cleaning processis performed to remove the abrasive particles from the semiconductorsubstrate and the top ring without changing a pH of the liquid attachedto the semiconductor substrate and the top ring, and then the cleaningliquid is gradually shifted from alkali to neutrality and the pH of theliquid attached to the semiconductor substrate and the top ring isshifted to neutrality. Therefore, the surface of the semiconductorsubstrate is returned to neutrality in such a state that the liquidattached to the semiconductor substrate still contains abrasiveparticles without pH shock. Therefore, abrasive particles are preventedfrom being aggregated on the semiconductor substrate and the top ring.Further, contamination of the semiconductor substrate and the top ringcaused by such abrasive particles is also prevented.

[0048] After this primary cleaning is completed, the top ring 74 ismoved toward the turntable 72, and the arm of the robot 86 b is moved tothe pusher 10 and holds the semiconductor substrate W. The robot 86 btransfers the semiconductor substrate W to the cleaning apparatuses 90a, 90 b and 90 c, and the subsequent cleaning processes are conductedtherein using pure water. A new semiconductor substrate W is placed onthe pusher 10 by the robot 86 b, and the top ring 74 is moved above thepusher 10 and holds the semiconductor substrate W, and then thesubsequent polishing of the new semiconductor substrate W is carriedout.

[0049] In the above embodiment, the primary cleaning process of thesubstrate is conducted in the primary cleaning apparatus C provided inthe pusher 10. However, the primary cleaning process may be conducted bythe nozzle units provided above the turntable 72 or in the vicinity ofthe turntable 72. Further, the primary cleaning process may be conductedin the cleaning apparatuses 90 a, 90 b and 90 c. That is, in the pusher10 and the cleaning apparatuses 90 a, 90 b and 90 c, the cleaning liquidmay be stepwise shifted from the cleaning liquid having substantiallythe same pH as the abrasive liquid or similar pH to the abrasive liquidto pure water.

[0050] Next, a dressing method according to another embodiment of thepresent invention will be described with reference to FIG. 7. As shownin FIG. 7, the dressing process is conducted between the polishingprocesses in such a manner that a dressing tool 94 is pressed againstthe polishing cloth 70 while a dressing liquid is supplied from adressing liquid supply nozzle 92 to the polishing cloth 70. In thisembodiment, a dressing liquid having substantially the same pH as theabrasive liquid or similar pH to the abrasive liquid is supplied fromthe first cleaning liquid tank 42 shown in FIG. 4 to the polishing cloth70. Thus, when the dressing liquid is supplied to the polishing cloth70, the pH of the abrasive liquid remaining on the location where thedressing liquid is supplied is not greatly changed to thus prevent theabrasive particles from being aggregated.

[0051] In the dressing process, by supplying the dressing liquid havingsubstantially the same pH as the abrasive liquid or similar pH to theabrasive liquid to the polishing cloth until a subsequent polishing of asubstrate is started, the subsequent polishing of the substrate can bestarted in a stable condition.

[0052] In the above embodiments, the primary cleaning process has beendescribed in the case where silica slurry is used as an abrasive liquid.If alumina (Al₂O₃) particles are used as abrasive particles, they areliable to being aggregated in a pH of 8 to 9, and hence it is necessaryto control a pH of the abrasive liquid in the same manner as silicaslurry or in the manner milder than the silica slurry.

[0053] In alumina slurry which is generally used for polishing thesemiconductor substrate W, alumina (Al₂O₃) particles as abrasiveparticles are stable in acidic solution having a pH of about 4 and formsecondary particles having a diameter of about 0.2 μm. In alumina slurrywhich is practically used, nitric acid solution is mainly used as acidicsolution. In alumina slurry which is practically used for polishing,α-alumina is mainly used as abrasive particles. Although α-alumina isstable in a pH of 7 or below, it is desirable that α-alumina has a pH of3.5 to 5. Since a-alumina is liable to being aggregated in a pH of 8 to9, the liquid having the pH range 8-9 is not desirable as a cleaningliquid. Therefore, the liquid having a pH of 7 or below is preferable asa cleaning liquid, and the liquid having a pH of 3.5 to 5 is quitefavorable.

[0054] As is apparent from the above description, according to thepresent invention, the pH of an abrasive liquid attached to thesubstrate or the polishing tool such as the top ring is not rapidlychanged, and hence abrasive particles contained in the abrasive liquidare not aggregated by pH shock. Thus, the cleaning of the substrate orthe dressing of the polishing cloth can be efficiently conducted.

[0055] Although certain preferred embodiments of the present inventionhave been shown and described in detail, it should be understood thatvarious changes and modifications may be made therein without departingfrom the scope of the appended claims.

What is claimed is:
 1. An apparatus for polishing and then cleaning a substrate, said apparatus comprising: a polishing apparatus for polishing a substrate using an abrasive liquid containing abrasive particles; and a cleaning apparatus for cleaning a polished surface of the substrate by supplying a cleaning liquid having the same pH as the abrasive liquid or similar pH to the abrasive liquid and then changing the pH of the cleaning liquid toward neutral so that the pH of the abrasive liquid attached to the polished surface of the substrate is not rapidly changed.
 2. An apparatus according to claim 1 , wherein said polishing apparatus has a polishing surface for polishing the substrate by contacting the substrate with said polishing surface, and said apparatus further comprising a dressing apparatus for dressing said polishing surface by supplying a dressing liquid having the same pH as the abrasive liquid or similar pH to the abrasive liquid so that the pH of the abrasive liquid on the polishing surface is not rapidly changed.
 3. An apparatus for polishing and then cleaning a substrate, said apparatus comprising: a polishing apparatus for polishing a substrate using an abrasive liquid containing abrasive particles; and a cleaning apparatus for cleaning a polished surface of the substrate by supplying a cleaning liquid having the same pH as the abrasive liquid or similar pH to the abrasive liquid and then changing the pH of the cleaning liquid toward neutral so that the pH of the abrasive liquid remaining on the polished surface of the substrate after polishing is not rapidly changed.
 4. An apparatus according to claim 3 , wherein said polishing apparatus has a polishing surface for polishing the substrate by contacting the substrate with said polishing surface and said apparatus further comprising a dressing apparatus for dressing said polishing surface by supplying a dressing liquid having the same pH as the abrasive liquid or similar pH to the abrasive liquid so that the pH of the abrasive liquid on the polishing surface is not rapidly changed.
 5. An apparatus for polishing and then cleaning a substrate, said apparatus comprising: a polishing apparatus for polishing a substrate using an abrasive liquid containing abrasive particles; and a cleaning apparatus for cleaning a polished surface of the substrate by supplying a cleaning liquid having the same pH as the abrasive liquid or similar pH to the abrasive liquid.
 6. An apparatus according to claim 5 , wherein said cleaning liquid is neutral.
 7. An apparatus according to claim 5 , wherein said cleaning apparatus further comprises a cleaning nozzle operable to eject said cleaning liquid.
 8. An apparatus according to claim 7 , wherein said cleaning apparatus further comprises a cover for preventing said cleaning liquid from being scattered.
 9. An method for polishing and then cleaning a substrate, said method comprising: polishing a substrate using an abrasive liquid containing abrasive particles; and cleaning a polished surface of the substrate by supplying a cleaning liquid comprising electrolytic ionic water and having the same pH as the abrasive liquid or similar pH to the abrasive liquid and then changing the pH of the cleaning liquid toward neutral so that the pH of the abrasive liquid attached to the polished surface of the substrate is not rapidly changed.
 10. An method for polishing and then cleaning a substrate, said method comprising: polishing a substrate using an abrasive liquid containing abrasive particles; and cleaning a polished surface of the substrate by supplying a cleaning liquid comprising electrolytic ionic water and having the same pH as the abrasive liquid or similar pH to the abrasive liquid and then changing the pH of the cleaning liquid toward neutral so that the pH of the abrasive liquid remaining on the polished surface of the substrate after polishing is not rapidly changed. 